1. Technical Field
This invention relates to a photo-optical keyboard and more particularly, to a photo-optical keyboard having molded common light transmission members which may be readily assembled into a keyboard.
2. Background Art
Prior art photo-optical keyboards generally comprise a matrix of keys arranged so that downward depression of any single key interrupts the passage of light being transmitted between a light source and a photosensor. Since the keys are arranged in a row-column matrix, there is generally a light source and a corresponding sensor for each row and for each column. A check of both the row and column sensors is made to indicate the identity of the depressed key. Although such keyboards correctly indicate the properly depressed key, they fail to provide an N key roll-over function. That is, if two or more keys in the same rows and/or columns are simultaneously depressed, the system cannot distinguish the third such depressed key. These types of keyboards often may be readily assembled from molded parts having common light transmission members providing a manufacturing advantage.
U.S. Pat. No. 3,856,127 teaches a matrix keyboard arrangement in its FIG. 7-8 embodiment having a light source associated with each row of keys and a photosensor associated with each column of keys. Individual bundles of optical fibers are arranged to emanate from each light source, and traverse along a row with individual fibers in each bundle terminating at different column positions adjacent a switch interrupter.
Second bundles of optical fibers emanate from each sensor and traverse along each column with individual fibers of each bundle terminating at different row positions adjacent a switch interrupter. The row light sources are sequentially energized so that actuation of any switch interrupter having an optical fiber adjacent thereto leading from the energized light source causes an interruption of light transmitted through the adjacent column optical fiber to the column sensor associated with that switch. Thus, multiple switches in the same row can be energized thereby providing multiple indications of key depressions to the corresponding multiple column sensors. Further, multiple simultaneous key depression in the same column provides a timed sequential output signal to the same column sensor thereby indicating all of the keys depressed. This keyboard thus has N key roll-over capability. However, the keyboard is very complex in its assembly since each column optical fiber must be precisely aligned with each corresponding row optical fiber so that key actuation provides a light interrupt. Further, each fiber must be properly placed relative to the light sources and sensors and hand routed through the keyboard assembly. Additionally, the fibers must be properly tied to the machine frame in order to prevent machine vibrations from displacing the critically placed fibers. The keyboard is thus difficult to assemble and to maintain in proper working order.